1. Field of the Invention
The present invention relates to the field of improved stress tolerance of plants, more specifically to genes and promoter sequences expressing at low temperatures and even more specifically to low temperature tolerance improved by means of gene transfer.
2. Background
Low temperature is one of the major limiting factors of growth, development and geographical distribution of plants. Some plants are able to acclimate by increasing their freezing tolerance upon exposure to low non-freezing temperature. This process involves physiological and biochemical changes, many of which are regulated through qualitative and quantitative modification of gene expression leading to the accumulation of newly synthesized proteins and mRNAs.
A number of genes having expression induced by low temperature have been isolated and characterized in a wide range of species. Most of the studies of gene expression during cold acclimation have been performed in plants from temperate and semi-temperate climates. Differently to this approach, our approach has been to study gene expression of genes induced by cold acclimation in a highly freezing tolerant plant. Deschampsia antarctica Desv. (Poacea) is a highly tolerant plant to the harsh freezing conditions and it is one of the two vascular plant species that have naturally colonized Maritime Antarctic Peninsula. A high accumulation of soluble carbohydrates, especially sucrose and fructans has been found in leaves of D. antarctica during growth period in the Antarctic summer. Total protein extracts from leaves of D. antaratica growing in the Antarctica has been shown to have a high cryoprotective activity on barley chloroplasts. Membrane lipid contents and the degree of unsaturation of fatty acids in the leaves do not differ significantly from plants in temperate zones. The optimal photosynthetic activity of this species is at 13° C. and it can maintain up to 30% of this rate at 0° C. Cold acclimation experiments have shown that D. antarctica is able to acclimate from −14.8° C.(LT50 at −14° C.) to −26.8° C. when growing at +2/−1.5° C. for 21 days in a solid substrate in the laboratory.
Due to the high capacity of cold acclimation that this species possesses we were interested of its gene expression during the acclimation. Not only is there a need to characterize genes that are responsible for low temperature tolerance of plants but there is also a need for characterization and identification of new plant promoters. Characterization and identification of such genes and their promoters will be greatly useful in the improvement of various crops. There is a clear need to improve low temperature tolerance of various sensitive plant species. Furthermore, in plant breeding and research there is a constant need for plant promoters inducible by various environmental factors such as low temperature.
Therefore, one object of the present disclosure is to increase cold resistance or tolerance of plants through gene transfer, especially of fruit trees such as, but not limited to eucalyptus, avocado, orange and peach trees. The system can be applied both to monocots and to dicots.
Another object of this invention is to reduce photo inhibition caused by chilling temperatures.
Still another object of the present invention is to provide transgenic plants, plant cells, plant tissue, plant organs or plant components of plants such as, but not limited to Arabidobis thaliana or Eucalyptus globulus carrying a recombinant transgene capable of expressing a modified transcript of a related-to-ubiquitin protein of Deschampsia antarctica. 
An even further object of the present invention is to provide promoters inducible by low temperatures, wounding and auxin treatment. Eucalyptus globulus has become one of the most important forest species, for example, in Chile due to its fast growth and good wood quality especially for the purposes of pulp manufacturing. Currently, it represents the second most planted species in Chile, amounting approximately, along with other eucalyptus species, to a total of 350,000 hectares. However, strong world market competition makes it necessary to develop better technologies for its cultivation. Despite of its excellent characteristic there are wide surface areas of up to 2 million hectares where growth limiting restrictions are found. In particular areas, such as foothills of Andean Mountains and Chile's Center Valley, the poor cold tolerance of Eucalyptus species has been a limiting factor to expand cultivation.
The present disclosure resolves the problem of low freezing tolerance of trees such as eucalyptus by a method rendering transgenic plants able to tolerate lower temperatures. In addition to eucalyptus this method is applicable to various low temperature susceptible plants such as peach.